Multiplex-signaling system



Jan. 13. 19225 1523,12?

B. w. KENDALL MULTIPLEX SIGNALING SYSTEM Filed Oct. 2, 1920 2Sheets-Sheet I puns UUU

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B. W. KENDALL MULTIPLEX S IGNALING SYSTEM Filed Oct. 2, 1920 2Sheets-Sheet 2 H //7V8/775F Burfon W Kenda/A y 24%;: AW

Patented Jan. 13 1 925.

BURTON W. KENDALL, OF NEW YORK, N. Y., A SSIGNOR TO WESTERN ELECTRICCOM- PANY, INCORPORATED, OF NEW YORK, N. Y., A CORPORATION OF NEW YORK.

MULTIPLEX SIGNALING SYSTEM.

Application filed October 2, 1920. Serial No. 4; 1 4,292.

To all whom it may concern:

Be it known that I, BURTON W. KENDALL, a citizen of the United States,residing at New York, in the county of New York and State of New York,have invented certain new and useful Improvements in Multiplex-Signaling Systems, of which the following is a full, clear, concise, andexact description.

This invention relates to multiplex signaling systems and moreparticularly to signaling systems in which a plurality of Morse codemessages may be simultaneously transmitted over a common circuit each asvariations or interruptions of oscillations of a particular frequencyindividual to that message.

A feature of the invention consists in the provision of a common trunlr"line or-link circuit with apparatus permitting it to servesimultaneously to connect a number of pairs of two-way Morse telegraphlines.

A further feature of the invention consists in the provision of amultiplex signaling system using oscillations of an ndividual frequencyfor each message, with means for translating the difierent frequencyoscillations into other oscillations of relatively large frequencydifi'erence. I

According to this invention, a common transmission circuit or trunk lineis associated with a plurality of Morse lines in such manner that eachMorse line repeats its outgoing message impulses to the transmissioncircuit as oscillation trains of corresponding duration and of anoscillation frequency peculiar to that particular Morse line. The commontransmission circuit repcats to each Morse line as Morse code i mpulsesof corresponding duration, each mcoming oscillation trains as are of theosc1llation frequency peculiar to that particular Morse line. In orderto repeat the Morse impulses to the transmission circuit, the receivingrelay of the Morse line is caused to control the association of anoscillator with the transmission circuit so that ,when the relay isenergized by a code impulse, the oscillator is operatively associatedwith the circuit and transmits tlicreover a train of waves of itsdistinctive frequency. The oscillators are associated by individualcircuits with the transmission circuit in such manner that the operationof each is unaflected by the others. The receiving chanmon transmissioncircuit to the Morse lines are each selective of oscillations of apartic-- ular frequency to the substantial ex clusion of those ofdifferent frequency. In order .to increase the relative difference infrequency of two adjacent frequency transnussions,-the incomingoscillations may be combined with oscillations produced by anothersource, preferably at the receiver, in order to secure oscillations ofthe dilference frequency of said incoming oscillations and said locallyproduced oscillations, These resultant difi'erence fr uency oscillationsma be made to differ 1n frequency by relative y larger amounts than thetrans mitted oscillations and are thus more readily separable.

In the drawing, Fig. 1 illustrates diagrammatically circuit arrangementsfor assoclating one terminal of a common transmission circuit with apluralit of Morse lines .for multiplex operation; ig. 2 illustrates amodified system in which an individual hybrid coil is provided for eachMorse line; Fi 3, a further modification in which a loca source at thereceiver produces oscillations to interact with the receivedoscillations; and Fig. 4 is a detail diagram of the device fortranslating oscillation trains into impulses.

Referring to Fig. 1, a terminal of a Morse line 1 with the usualartificial line A is shown associated with the terminal of a commontransmission circuit 2. Receivin relay 3 of the -Morse line whenenergize operates its armature 4 to close the circuit of a relay 5, thearmatures 6 of which are connected to the terminals of an alternatingcurrent source 0, preferably, although not necessarily, of the electrondischarge type. hen energized, relay 5 connects the oscillation source 0to a tuned loop circuit 8 inductively connected to an outgoing channel 9by a branch circuit 10, which, as in the case of the circuit 8, ispreferably tuned to the frequency of source Although but a single Morseline is illustrated, it is understood that a plurality of such lines areprovided, each havingits individual receiving relay and individualoscillator controlled thereby to supply oscillations of a frequencyindividual to that oscillator to a correspondin'gly tuned circuit 8associated with the outgoing channel 9.

I connected with circuit 2 with respect to the outgoing channel by aninductive coupling with the bridge circuit of the hybrid coil.Associated with the incoming channel and preferably, although notnecessarily, bridged thereacross, are a plurality of selective divices13 corresponding in their selectivity to the tuned circuits 8 and 10.These selective devices may take the form of the circuits 8, 10associated with the outgoing channel or may be. as illustrated,

band filters of the general type disclosed in U. S. Patent 1,227,113 toCampbell. The characteristic of these filters is such that they transmitcurrents of a given range of frequencies with substantially negligibleattenuation and suppress currents of frequencies outside the givenrange. This range may be made very small but is preferably sufiicientlywide to permit slight variations in the generator frequency. Currentsselected and transmitted by band filter 13 are impressed'upon the inputcircuit of a translating device D, the function of which is to receiveoscillation trains and .to translate them into impulses of correspondingduration. Translating device D, when operated, supplies an energizingimpulse to a transmitting relay 14 which operates to close the ordinaryMorse transmitting circuit 15 to cause direct current source 16 toimpress code impulses on Morse line 1. The operation of this arrangementis as follows: Morse code impulses impressed on line 1 at a distantpoint energize receiving. relay 3, which in turn closes the energizingcircuit of rela 5, thus connecting oscillator O to outgoing channel 9.If, for example, the oscillator is producing oscillations of 8,000cycles frequency, a train of waves of that frequency will be transmittedout over circuit 2. The duration of this train will correspond to thatof the code impulse on line 1. At the distant terminal of circuit 2. theapparatus is similar to'that at the terminiil associated with line 1 andincludes several Morse lines, one of which. corresponds to line 1. Theoperation of this corresponding line and its apparatus in receiving maybe clear from a consideration of the receiving 0 eration of line 1. Atrain of incoming oscillations of 8,000 cycle frequency arrivin overcircuit 2 is transferred from the bridge of the hybrid coil 11 toincoming channel 12. Of the various filters 13 connected with chan nel12 all except that associated with line 1 are so designed as to excludecurrents of 8,000 cycle frequency. -The train of oscillations istherefore impressed upon the input circuit of only the translatingdevice I) which causes an impulse of corresponding duration to besupplied. from .its output circuit to transmitting relay 14 whichrepeats the impulse to line 1. In thismanner two Morse lines connectedto opposite terminals of the common transmission circuit 2 are enabledto carry on' two-way inter-communication over circuit 2 by means of the8,000-cycle oscillations. As many pairs of Morse lines as are desiredmay thus be connected, the two lines of each pair being connected to theopposite ter-' minals of circuit 2. It will be understood that each pairof lines employs oscillations of an individual frequency and that thevarious selecting circuits 8, 10, and 13 are transmission to the samelow frequency line. It is therefore possible to carry on an indefinitenumber of simultaneous twoway transmissions over the common transmissioncircuit 2 depending upon the transmission characteristics of thiscircuit for oscillations and the, frequency difference which isnecessary for separation of the oscillations of adjacent channels.

In Fig. 2 a Morse line is illustrated connected to common transmissioncircuit 22 by channels similar to those employed in the arrangement ofFig. 1 except that an individual hybrid coil is used for each of theMorse lines and the band filters are connected between the commontransmission circuit 22 and their respective hybrid coils. In thisarrangement a network N is provided for each channel to simulate theimpedance of the circuit 22 and its associated circuits as viewed fromhybrid coil 19 for currents of the frequency traversing the hybrid coil.Incoming channel 17 includes translating device D and relay l4 andoutgoing channel 18 comprises normally disconnected oscillator O. In allessential respects the operation of these Morse circuits is the same asin the previously described arrangement and accordingly requires nofurther explanation.

Where it is desired to use the common transmission circuit 22 forordinary telephony or in effect to composite the system just describedon an ordinary trunk line 22,

an ordinary talking circuit including the subscribers station shownconventionally as comprising a transmitter 20, a source 24 and areceiver 21 may be connected to circuit 22 by a filter 23 whichtransmits with substantially negligible attenuation currents of theessential speech frequency and substantially extinguishes currents offrequencies differing appreciably therefrom. The transmission bandfilter 23 may he giv-- en various limits but it may be stated that inpractice the range of from 100 to 2200 cycles is in generalsatisfactory. The Morse channels associated with filters 13 of Fig. 2may therefore employ oscillation frequency exceeding 2200 or less than100 cycles in frequency. In some cases it is desirable to reserve therange of frequencies below 100 cycles for ordinary Morse signals whichmay be transmitted directly over the common transmission. circuit as inthe case of ordinary composited lines.

The circuits of Fig. 3 are in general similur to those of Fig. 1 withthe exception that a frequency reduction a paratus is introduced betweenthe circuit 2 and incomingchannel 12. This consists of a balancelarrangeinent of evacuated electron discharge devices 24 having their ridcircuits oppositely related to the bri ge circuit of the hybrid coil 11so that one grid will tend to become positive with respect to the commonfilament potential when the other ismade negative and vice versa.Similarly, the plate circuits of these electron discharge devices areoppositely connected to the incoming channel 12, that is, so that anincrease in the current of one tends to annul the effect of an increasein the current of the other so far as channel 12 is concerned. A localsource 25 of sinusoidal oscillations is connected to both electrondischarge devices and as illustrated may be inductively associated witha transformer winding 26 in a common branch of their "grid circuits.

This arrangement is similar to the wellknown combiner disclosed andfully explained in British Patent No. 131,426. It will be suflic'ient topoint out that its characteristics are such that it does not transmitoscillations supplied by source 25 but when oscillations are receivedfrom hybrid coil 11, it transmits oscillations of the sum; frequency andother oscillations of the difference frequency of the .localoscillations and the incoming oscillations. If, for

example. three Morse lines at the-remote end of circuit 2 transmitthereover oscillations ofv 6500, 7000 and 7500 cycles, respectively, andthe local oscillator 25 operates to produce oscillations of 8000 cycles,there will appear in channel 12, when all three Morse circuits aresimultaneously operated, difference frequency currents of 1500, 1000 and500 cycles respectively, corresponding to impulses from the three remoteMorse lines. These difference frequency currents are much more readilyseparable than are the original currents transmitted over the circuit 2,for the reason that their relative frequency difference is larger. Forexample, the intermediate original frequency 7000 differs from the othertwo original frequencies 6500 and 7500 by less than 10% and thecorresponding intermediate difference frequency, namely, 1000 cycles,differs from the other two difference frequenare first separated fromthe various other currents which then pass to the frequency reduction aparatus.

The trans ating device for receiving wave trains and producinguni-directional impulses of corresponding duration, shown conventionallyin the first three figures by the rectangle D, is illustrated in detailin Fig. 4. It comprises two thermionic repeaters preferably of thehighly evacuated three-element type, the first serving to amplify thewave train and the second operating in response to the amplified wavetrain to control relay 14. The normal potential of the grid or controlelement of the second repeater 30 is determined by a polarizing source31, and the plate current voltage is obtained by a variable connectionto source 32 which supplies plate current to the first repeater. It istherefore possible to so adjust the circuits that the incomingoscillations will cause an increase in the average value of the spacecurrent, thus operating the marginal relay 14. It is also possible tomake such adjustments that the average value of the space current isdecreased. With this latter arrangement the marginal relay wouldnormally be energized and would release its armature during the wavetrain. 7

The invention has been described as embodied in conductive signalinsystems but it is to be understood that alt ough of par-' ticularutility in multiplex Morse code signaling over wire lines, theprinciples of the invention are applicable as well to energytransmission generally, whether by radiant energy or energy transmittedover conductive circuits.

\Vhat' is claimed is:

1. In combination a multiplex wave transmission circuit, a plurality ofcontinuously active wave sources of different fre quenciesfor saidcircuit, distant outlying stations, :1 direct current telegraph lineextending from each of said stations for cooperating with saidtransmission circuit in the trans-- mission of signals and'a relayactuated from each station by telegraphicimpulses on the correspondingline for controlling the application to and withdrawal from saidtransmission circuit of the wave from the corresponding source, for timeeriods in accordance with the length of sai impulses.

2. In a telegraph system distantly sep arated main stations, a multiplexcarrier line interconnecting said stations, a number of outlyingstations connected with each main station by direct current telegraphlines terminating in Morse telegraph receiving and sending setsincluding relays, a number of continuously active Wave sources at eachof said main stations for furnishing waves of different frequencies fortransmission over said multiplex carrier current line, carrier currentreceiving circuits at ,rent receiving relay, said Wave sources at therespective main stations -a nd the carrier current receiving circuitsbeing allotted so that an outlying station transmits signals to andreceives signals from a given outlying station that is associated withanother main station. through the medium of said multiplex carriercurrent line and by means of a wave source and a carriercurrentreceiving circuit at each main station.

In witness whereof, I hereunto subscribe my name this 28th day'ofSeptember, A. D.. 1920.

BURTON WV. KENDALL;

